555Timer. - Circuit Schematic Two-Door Buzzer with Display using IC NE555N or LM555 . The Two-door Buzzer with Display is applicable and well suited to be used in a house having two gates or doors that are distant from each other. It helps the person inside the house by providing an alarm and a number display determining which door where the visitor is. It also saves time and effort as the owner does not need to check both doors.
The circuit is basically made up of a monostable and astable multivibrators (a.k.a free-running multivibrator). I suggest you read more about these fascinating timers. Okay, let’s cut right to the chase! The monostable multivibrator provides the timing on how long the buzzer would go while the astable multivibrator provides the nice alarm tone. You can change the frequency of the alarm tone produced by the astable multivibrator by rotating the potentiometer (R18 in the circuit). Please read more about Circuit Schematic Two-Door Buzzer with Display using IC NE555N or LM555 from original article.
The Original Article : "Two-Door Buzzer with Display"